Distance measurement system and method thereof

ABSTRACT

A light source transmits detecting light toward an object. The object reflects the detecting light and forms a reflected light. A sensor is used for sensing the reflected light. Then, an exposure control unit coupled to the sensor performs luminance convergence on the reflected light according to luminance of the reflected light sensed by the sensor. And a distance measurement device coupled to the sensor detects a distance between the object and the light source and/or the sensor according to an image position of the reflected light on the sensor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a distance measurement system andmethod thereof, and more particularly, to a distance measurement systemand method thereof capable of utilizing an automatic exposure-controlmechanism to increase dynamic range of an exposure time, and a signal tonoise ratio.

2. Description of the Prior Art

In the prior art, a distance measurement device transmits detectinglight toward an object, and receives reflected light generated by theobject reflecting the detecting light, and then calculating a distancebetween the object and the distance measurement device according to animage position of the reflected light on a sensor. However, when thedistance measurement device sensed the reflected light reflected by theobject, an exposure control unit of the distance measurement device cannot automatically adjust an exposure time of the sensor, a sensing modeof the sensor, an output signal gain of the sensor, and/or supplycurrent of a light source with luminance of the reflected light, so thatthe distance measurement device can not increase dynamic range of theexposure time of the sensor, and a signal to noise ratio. In addition,the distance measurement device cannot automatically adjust the exposuretime of the sensor, the sensing mode of the sensor, the output signalgain of the sensor, and/or the supply current of the light source, so asto cause the exposure time of the sensor to be over-saturated orinsufficient resulting in the distance measurement device gainingincorrect measurement distance and lower power efficiency.

SUMMARY OF THE INVENTION

An embodiment provides a distance measurement system. The distancemeasurement system includes a light source, a sensor, an exposurecontrol unit, and a distance measurement device. The light source isused for transmitting detecting light toward an object, where thedetecting light is reflected by a surface of the object to formreflected light. The sensor is used for sensing the reflected light. Theexposure control unit is used for performing luminance convergence onthe reflected light according to luminance of the reflected light sensedby the sensor. And the distance measurement device is used for detectinga distance between the object and the light source and/or the sensoraccording to an image position of the reflected light on the sensor.

Another embodiment provides a method of distance measurement. The methodincludes utilizing a light source to transmit detecting light toward anobject, wherein the detecting light is reflected by a surface of theobject to form reflected light; utilizing a sensor to sense thereflected light; performing luminance convergence on the reflected lightaccording to luminance of the reflected light sensed by the sensor; anddetecting a distance between the object and the light source and/or thesensor according to an image position of the reflected light on thesensor.

The present invention provides a distance measurement system. Thedistance measurement system is capable of automatically adjusting anexposure time of a sensor, a sensing mode of the sensor, an outputsignal gain of the sensor, and/or supply current of a light source fordifferent application conditions for controlling luminance of reflectedlight sensed by the sensor not to be over-saturated or insufficient.Therefore, the distance measurement system can increase accuracy of thedistance measurement, dynamic range of the exposure time of the sensor,and a signal to noise ratio.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a distance measurement system accordingto an embodiment of the present invention.

FIG. 2 is a diagram illustrating the sensor sensing a first image and asecond image respectively when the light source is turned on or off andthe identification device comparing the first image with the secondimage to determine the reflected light which is reflected to the sensorby the surface of the object.

FIG. 3 is a diagram illustrating the exposure control unit performingluminance convergence on the reflected light according to luminance ofthe reflected light sensed by the sensor.

FIG. 4 is a diagram illustrating a relationship between the luminance ofthe reflected light sensed by the sensor and an exposure value after theexposure control unit performs the luminance convergence on thereflected light.

FIG. 5 is a diagram illustrating a distance measurement system accordingto another embodiment of the present invention.

FIG. 6 is a flowchart illustrating a method of distance measurementaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1. FIG. 1 is a diagram illustrating a distancemeasurement system 100 according to an embodiment of the presentinvention. The distance measurement system 100 includes a light source102, a first lens 104, a second lens 106, a sensor 108, anidentification device 110, an exposure control unit 112, and a distancemeasurement device 114. The light source 102 is used for transmittingdetecting light toward an object, where the light source 102 is an IRLED light source. The second lens 106 is installed between the lightsource 102 and the object for focusing the detecting light on thesurface of the object, and the focused detecting light is reflected bythe surface of the object to form reflected light. The first lens 104 isinstalled between the sensor 108 and the object for focusing thereflected light on the sensor 108. The sensor 108 is used for sensingthe focused reflected light, where the sensor 108 senses a first imagewhen the light source 102 is turned on, and senses a second image whenthe light source 102 is turned off. The identification device 110 iscoupled to the sensor 108 for comparing the first image with the secondimage to identify an image position of the reflected light reflected bythe object on the sensor 108. The exposure control unit 112 is coupledto the sensor 108 for performing luminance convergence on the reflectedlight according to luminance of the reflected light sensed by the sensor108 and the image position of the reflected light, so as to cause theluminance of the reflected light sensed by the sensor 108 not to beover-saturated or insufficient. The distance measurement device 114 iscoupled to the sensor 108 for detecting a distance between the objectand the light source 102 and/or the sensor 108 by the triangulationmeasurement method according to the image position of the reflectedlight on the sensor 108.

Please refer to FIG. 2. FIG. 2 is a diagram illustrating the sensor 108sensing a first image 202 and a second image 204 respectively when thelight source 102 is turned on or off and the identification device 110comparing the first image 202 with the second image 204 to determine thereflected light which is reflected to the sensor 108 by the surface ofthe object. As shown in FIG. 2, the first image 202 includes brightspots 206, 208 caused by background light sources and a bright spot 210caused by the object. The second image 204 only includes the brightspots 206, 208 because the light source 102 is turned off. Therefore,the identification device 110 excludes the bright spots 206, 208 aftercomparing the first image 202 with the second image 204 to obtain athird image 212 only including the bright spot 210 caused by the object.

Please refer to FIG. 3 and FIG. 4. FIG. 3 is a diagram illustrating theexposure control unit 112 performing the luminance convergence on thereflected light according to the luminance of the reflected light sensedby the sensor 108. FIG. 4 is a diagram illustrating a relationshipbetween the luminance of the reflected light sensed by the sensor 108and an exposure value after the exposure control unit 112 performs theluminance convergence on the reflected light. When a distance betweenthe object and the distance measurement system 100 is too long so thatthe luminance of the reflected light sensed by the sensor is too low,the exposure control unit 112 first increases exposure time of thesensor 108. If an exposure value is still insufficient after theexposure time of the sensor 108 is extended to a first predeterminedtime (A point in FIG. 3), a sensing mode of the sensor 108 is switchedto a high sensitivity mode and the exposure time of the sensor 108 isadjusted down from the first predetermined time to a first adjustingvalue. If the exposure value is still insufficient, the exposure time ofthe sensor 108 is increased from the first adjusting value. When theexposure time of the sensor 108 is equal to the maximum exposure time ofthe sensor 108, the exposure control unit 112 starts to increase anoutput signal gain of the sensor 108. So as shown in FIG. 4, arelationship between the luminance of the reflected light sensed by thesensor 108 and the exposure value is linear after the exposure controlunit 112 adjusts the luminance of the reflected light. In addition, theexposure control unit 112 can also adjust supply current of the lightsource 102 for increasing the luminance of the detecting lighttransmitted by the light source 102, and the luminance of the reflectedlight. But the present invention is not limited to start to increase theoutput signal gain of the sensor 108 when the exposure time of thesensor 108 is equal to the maximum exposure time of the sensor 108. Theoutput signal gain of the sensor 108 starts to be increased when theexposure time is not equal to the maximum exposure time of the sensor108 yet in another embodiment of the present invention.

In addition, when the distance between the object and the distancemeasurement system 100 is too short so that the luminance of thereflected light sensed by the sensor is too high, the exposure controlunit 112 first decreases the output signal gain of the sensor 108 forreducing the luminance of the reflected light. If the luminance of thereflected light sensed by the sensor 108 is still too high, the exposurecontrol unit 112 further decreases the exposure time of the sensor 108.If the exposure value of the sensor 108 is still too high after theexposure time of the sensor 108 is reduced to a second predeterminedtime (B point in FIG. 3), the sensing mode of the sensor 108 is switchedto a low sensitivity mode and the exposure time of the sensor 108 isadjusted up from the second predetermined time to a second adjustingvalue. If the exposure value is still too high, the exposure time of thesensor 108 is decreased from the second adjusting value. So as shown inFIG. 4, the relationship between the luminance of the reflected lightsensed by the sensor 108 and the exposure value is linear after theexposure control unit 112 adjusts the luminance of the reflected light.In addition, the exposure control unit 112 can also adjust supplycurrent of the light source 102 for decreasing the luminance of thedetecting light transmitted by the light source 102, and the luminanceof the reflected light. But the present invention is not limited tofirst decrease the output signal gain of the sensor 108, and then adjustthe exposure time of the sensor 108. In another embodiment of thepresent invention, the exposure control unit 112 can also first adjustthe exposure time of the sensor 108 and then decrease the output signalgain of the sensor 108, or adjust the exposure time of the sensor 108and decrease the output signal gain of the sensor 108 at the same time.

Besides, the exposure control unit 112 may control the luminance of thereflected light sensed by the sensor 108 by automatically adjusting theexposure time of the sensor 108, the sensing mode of the sensor 108, theoutput signal gain of the sensor 108, and/or the supply current of thelight source 102 for different application conditions. For example, theexposure control unit 112 may adjust the luminance of the reflectedlight sensed by the sensor 108 to gray level 200 in some specificapplication conditions. In addition, the exposure control unit 112 mayalso increase dynamic range of the exposure time of the sensor 108 byadjusting the sensing mode of the sensor 108 (high, low sensitivitymode).

The distance measurement device 114 is coupled to the sensor 108 fordetecting the distance between the object and the light source 102and/or the sensor 108 by the triangulation measurement method accordingto the image position of the reflected light on the sensor 108 (X1, X2points in FIG. 1).

Please refer to FIG. 5. FIG. 5 is a diagram illustrating a distancemeasurement system 500 according to another embodiment of the presentinvention. The distance measurement system 500 includes a light source502, a first lens 504, a second lens 506, a sensor 508, an exposurecontrol unit 512, and a distance measurement device 514, where thesensor 508 further includes an IR filter 516. A difference between thedistance measurement system 500 and the distance measurement system 100is that the distance measurement system 500 does not have anidentification device. Because the IR filter 516 may filter lightoutside the IR range from entering the sensor 508, the sensor 508 canidentify directly reflected light which is reflected to the sensor 508by a surface of an object without sensing a first image (turning on thelight source 502) and a second image (turning off the light source 502).Further, subsequent operational principles of the distance measurementsystem 500 are the same as the distance measurement system 100, sofurther description thereof is omitted for simplicity.

Another embodiment of the present invention combines the above bothmethods of identifying the reflected light in the distance measurementsystem 100 and the distance measurement system 500, that is to say, asensor senses a first image (turning on the light source) and a secondimage (turning off the light source), and an IR filter identifies thereflected light at the same time. Further, subsequent operationalprinciples are the same as the distance measurement system 100 and thedistance measurement system 500, so further description thereof isomitted for simplicity.

Another embodiment of the present invention utilizes a laser source as alight source, so another embodiment of the present invention does notneed a first lens and a second lens to focus light (detecting light andreflected light). Further, subsequent operational principles are thesame as the distance measurement system 100, so further descriptionthereof is omitted for simplicity.

Please refer to FIG. 6. FIG. 6 is a flowchart illustrating a method ofdistance measurement according to another embodiment of the presentinvention. FIG. 6 uses the distance measurement system 100 in FIG. 1 toillustrate the method. Detailed steps are as follows:

Step 600: Start.

Step 602: The light source 102 transmits the detecting light toward theobject, and the second lens 106 focuses the detecting light on thesurface of the object.

Step 604: The first lens 104 focuses the reflected light which isreflected to the sensor 108 by the surface of the object.

Step 606: The sensor 108 senses the first image when the light source102 is turned on.

Step 608: The sensor 108 senses the second image when the light source102 is turned off.

Step 610: The identification device 110 compares the first image withthe second image to identify the reflected light reflected to the sensor108 by the surface of the object.

Step 612: The exposure control unit 112 performs the luminanceconvergence on the reflected light according to the luminance of thereflected light sensed by the sensor 108.

Step 614: The distance measurement device 114 determines the distancebetween the object and the light source 102 and/or the sensor 108according to the image position of the reflected light on the sensor108.

Step 616: End.

In Step 612, the exposure control unit 112 can control the luminance ofthe reflected light sensed by the sensor 108 not to be over-saturated orinsufficient by dynamically adjusting the exposure time of the sensor108, the sensing mode of the sensor 108, the output signal gain of thesensor 108, and/or the supply current of the light source 102 forincreasing the accuracy of the distance measurement device 114. Wheredetailed step of the exposure control unit 112 performing the luminanceconvergence on the reflected light as follows: when the luminance of thereflected light sensed by the sensor 108 is too low, the exposurecontrol unit 112 increases the exposure time of the sensor 108 until thefirst predetermined time (A point in FIG. 3). Meanwhile, the exposurecontrol unit 112 switches the sensing mode of the sensor 108 to the highsensitivity mode and adjusts the exposure time of the sensor 108 downfrom the first predetermined time to the first adjusting value, and thenincreases the exposure time of the sensor 108 from the first adjustingvalue. When the exposure time of the sensor 108 is equal to the maximumexposure time of the sensor 108, the exposure control unit 112 starts toincrease the output signal gain of the sensor 108. In addition, theexposure control unit 112 also increases the supply current of the lightsource 102 for increasing the luminance of the detecting light and thereflected light. In addition, when the luminance of the reflected lightsensed by the sensor is too high, the exposure control unit 112decreases the exposure time of the sensor 108 until the secondpredetermined time (B point in FIG. 3). Meanwhile, the exposure controlunit 112 switches the sensing mode of the sensor 108 to the lowsensitivity mode and adjusts the exposure time of the sensor 108 up fromthe second predetermined time to the second adjusting value, and thendecreases the exposure time of the sensor 108 from the second adjustingvalue. Moreover, the exposure control unit 112 also decreases the supplycurrent of the light source 102 for decreasing the luminance of thedetecting light and the reflected light.

Another embodiment of the present invention utilizes an IR source and anIR filter to identify reflected light, or utilizes a sensor to sense afirst image (turning on a light source) and a second image (turning offthe light source) and the IR filter to identify the reflected light atthe same time.

In addition, the embodiment of FIG. 6 also can utilize a laser source asalight source, so that the embodiment of FIG. 6 does not need a firstlens and a second lens to focus light.

To sum up, the exposure control unit of the distance measurement systemcan automatically adjust the exposure time of the sensor, the sensingmode of the sensor, the output signal gain of the sensor, and/or thesupply current of the light source for different application conditionsfor controlling the luminance of the reflected light sensed by thesensor not to be over-saturated or insufficient. Thus, the distancemeasurement system of the present invention can increase the accuracy ofthe distance measurement, the dynamic range of the exposure time of thesensor, and the signal to noise ratio.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

1. A distance measurement system, comprising: alight source fortransmitting detecting light toward an object, wherein the detectinglight is reflected by a surface of the object to form reflected light; asensor for sensing the reflected light; an exposure control unit forperforming luminance convergence on the reflected light according toluminance of the reflected light sensed by the sensor; and a distancemeasurement device for detecting a distance between the object and thelight source and/or the sensor according to an image position of thereflected light on the sensor.
 2. The distance measurement system ofclaim 1, further comprising: a first lens installed between the sensorand the object for focusing the reflected light on the sensor; and asecond lens installed between the light source and the object forfocusing the detecting light on the surface of the object.
 3. Thedistance measurement system of claim 1, further comprising: anidentification device for identifying the reflected light focused on thesensor by the first lens, wherein the sensor senses a first image whenthe light source is turned on, the sensor senses a second image when thelight source is turned off, then the identification device compares thefirst image with the second image to capture the reflected lightreflected to the sensor by the surface of the object.
 4. The distancemeasurement system of claim 1, wherein the light source is an IR lightsource and the sensor further comprises an IR filter for blocking lightoutside the IR range from entering the sensor.
 5. The distancemeasurement system of claim 1, wherein the exposure control unit adjustsexposure time of the sensor according to the luminance of the reflectedlight sensed by the sensor for increasing or decreasing a time period ofthe reflected light entering the sensor.
 6. The distance measurementsystem of claim 1, wherein the exposure control unit adjusts the sensorto operate in a high sensitivity mode or a low sensitivity modeaccording to the luminance of the reflected light sensed by the sensorfor adjusting efficiency of the sensor receiving the reflected light. 7.The distance measurement system of claim 1, wherein the exposure controlunit adjusts an output signal gain of the sensor after the sensor sensesthe reflected light according to the luminance of the reflected lightsensed by the sensor for amplifying or decaying a value outputted by thesensor representing the luminance of the reflected light.
 8. Thedistance measurement system of claim 1, wherein the exposure controlunit further adjusts supply current of the light source for increasingor decreasing luminance of the detecting light transmitted by the lightsource for further changing the luminance of the reflected lightentering the sensor.
 9. The distance measurement system of claim 1,wherein the light source is a light emitting diode or a laser source.10. A method of performing distance measurement, comprising: utilizing alight source to transmit detecting light toward an object, wherein thedetecting light is reflected by a surface of the object to formreflected light; utilizing a sensor to sense the reflected light;performing luminance convergence on the reflected light according toluminance of the reflected light sensed by the sensor; and detecting adistance between the object and the light source and/or the sensoraccording to an image position of the reflected light on the sensor. 11.The method of claim 10, further comprising: a first lens focusing thereflected light on the sensor; and a second lens focusing the detectinglight on the surface of the object.
 12. The method of claim 10, whereinutilizing the sensor to sense the reflected light comprises: utilizingthe sensor to sense a first image when the light source is turned on;utilizing the sensor to sense a second image when the light source isturned off; and comparing the first image with the second image tocapture the reflected light reflected to the sensor by the surface ofthe object.
 13. The method of claim 10, wherein the detecting light andthe reflected light are infrared (IR) light and the sensor furthercomprises utilizing an IR filter to block light outside the IR rangefrom entering the sensor.
 14. The method of claim 10, wherein performingthe luminance convergence on the reflected light comprises: increasingexposure time of the sensor until a predetermined time when theluminance of the reflected light sensed by the sensor is too low, andmeanwhile switching a sensing mode of the sensor to a high sensitivitymode and adjusting the exposure time of the sensor down from thepredetermined time to an adjusting value, then amplifying a light signalsensed by the sensor when the exposure time is increased from theadjusting value to the maximum exposure time of the sensor.
 15. Themethod of claim 14, wherein performing the luminance convergence on thereflected light further comprises: increasing supply current of thelight source before increasing the exposure time of the sensor forincreasing the luminance of the detecting light and the luminance of thereflected light.
 16. The method of claim 10, wherein performing theluminance convergence on the reflected light comprises: decreasingexposure time of the sensor until a predetermined time when theluminance of the reflected light sensed by the sensor is too high, andmeanwhile switching a sensing mode of the sensor to a low sensitivitymode and adjusting the exposure time of the sensor up from thepredetermined time to an adjusting value, and then adjusting theexposure time of the sensor down from the adjusting value.
 17. Themethod of claim 16, wherein performing the luminance convergence on thereflected light further comprises: decreasing supply current of thelight source before decreasing the exposure time of the sensor forreducing the luminance of the detecting light and the luminance of thereflected light.
 18. The method of claim 10, wherein performing theluminance convergence on the reflected light comprises: increasingexposure time of the sensor when the luminance of the reflected lightsensed by the sensor is too low, and decreasing the exposure time of thesensor when the luminance of the reflected light sensed by the sensor istoo high.
 19. The method of claim 10, wherein performing the luminanceconvergence on the reflected light comprises: switching a sensing modeof the sensor to a high sensitivity mode when the luminance of thereflected light sensed by the sensor is too low, and switching thesensing mode of the sensor to a low sensitivity mode when the luminanceof the reflected light sensed by the sensor is too high.
 20. The methodof claim 10, wherein performing the luminance convergence on thereflected light comprises: amplifying alight signal sensed by the sensorwhen the luminance of the reflected light sensed by the sensor is toolow, and decaying the light signal sensed by the sensor when theluminance of the reflected light sensed by the sensor is too high. 21.The method of claim 10, wherein performing the luminance convergence onthe reflected light comprises: increasing supply current of the lightsource when the luminance of the reflected light sensed by the sensor istoo low, and decreasing supply current of the light source when theluminance of the reflected light sensed by the sensor is too high.